The electromagnetic spectrum covers a wide range of wavelengths, among which are wavelengths visible to the human eye often referred to as the visible spectrum covering a range of from 380 nm to 780 nm. Some wavelengths of the electromagnetic spectrum including those of the visible spectrum provide harmful effects, while others are known to have beneficial effects on the eye. Some wavelengths of the visible spectrum are also known to induce a range of neuroendocrine, physiological and behavioural responses known as non-image-forming (NIF) responses.
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. This tissue has four main layers from the choroid to the vitreous humour: the retinal pigment epithelium (hereinafter referred to as “RPE”), the photoreceptor layer (including rods and cones), the inner nuclear layer with bipolar and amacrine cells, and finally, the ganglion cell layer which contains some intrinsically photosensitive ganglion cells (1% of retinal ganglion cells (hereinafter referred to as “RGC”)). This last cell type is important for circadian photoentrainment (biological rhythms) and pupillary function.
Neural signals initiate in the rods and cones, and undergo complex processing by other neurons of the retina. The output from the processing takes the form of action potentials in retinal ganglion cells, the axons of which form the optic nerve. Several important features of visual perception can be traced to the retinal encoding and processing of light.
Photobiology, which is the study of the biological effect of light, has established that a portion of the electromagnetic spectrum provides beneficial effects for good health, including visual perception and circadian functions. However, it has also established the importance of protecting the eyes against harmful radiation, such as ultraviolet (UV) rays. Visible light, even of ordinary everyday intensity, may cause retinal damage or contribute to the development of early and late Age-Related Maculopathy (ARM), such as Age-related Macular Degeneration (AMD). There are indications in some epidemiological studies that level of exposure to sunlight may be associated with the development of AMD: Tomany S C et al. Sunlight and the 10-Year Incidence of Age-Related Maculopathy. The Beaver Dam Eye Study. Arch Ophthalmol. 2004; 122:750-757.
Other pathologies are related to exposure to light. For example, the production of melatonin in circadian rhythms is known to be regulated by exposure to light. As a consequence, specific light modification in the environment might impact synchronisation of the body's biological clock. Migraines are associated with photophobia which is an abnormal intolerance to light stimulus of the visual system and epilepsy can be affected by the presence of light.
Ophthalmic devices that filter out with low selectivity harmful UV radiations are widely used. For example, sunglasses are designed to provide solar protection by protecting the eye against the harmful effects of UVA and UVB rays. Intraocular lenses (IDLs) with UV filters were introduced in the 1990s; these being mainly post-cataract surgery implants replacing the crystalline lens.
The present invention has been devised with the foregoing in mind.